1. Field of the Invention
The invention relates to a recording material having a substrate and a radiation-sensitive layer which contains a component absorbing IR radiation and which, after the action of infrared radiation, becomes soluble or at least swellable in an aqueous alkaline developer. The material is insensitive to white light. It is particularly suitable for the production of printing plates for offset printing.
2. Description of the Related Art
Recording materials whose radiation-sensitive layer is sensitive in the ultraviolet and/or visible range are conventionally used for the production of printing plates for offset printing. The layer is recorded on by means of radiation of appropriate wavelengths through a photographic negative and is then developed. Recent processes can be accomplished without such photographic negatives. The recording is then effected by means of laser beams from digitally controlled lasers, known as "computer-to-plate" processes. However, lasers which emit radiation in the range of visible light are relatively expensive and also require special recording materials. See, for example, EP-A 0 573 805 (=CA-A 2 097 038) and EP-A 0 704 764.
On the other hand, infrared lasers, in particular infrared laser diodes, are substantially more economical. However, recording materials which are sensitized in the IR range, i.e., in the range from about 700 to 1100 nm, are required for this purpose. Many of these IR-sensitized materials have the further advantage that they are not sensitive in the ultraviolet and visible range (referred to below as UV/VIS) and consequently can be processed in daylight or normal white artificial light. Examples of these are described in DE-A 25 12 038 (=GB-A 1 489 308), WO 90/12342 and EP-A 0 562 952, 0 580 393, and 0 773 112.
Materials which are sensitized both in the UV/VIS and in the IR range are also known (EP-A 0 625 728 and 0 672 954, WO 96/20429). They cannot of course be processed in normal illumination.